1. Field of the Invention
The present invention relates to cutting by use of a rotating axially-moving drill bit, and more particularly drill bits of the type having a central lead screw and integral elongated shank.
2. Brief Description of the Prior Art
Drill bits adapted to drill through wood over extended distances by use of integral elongated shanks are known. Specifically, a conventional drill bit including a spiral channel and radial cutting edge has been integrally connected to an elongated shank. Problems have developed in attempting to pass a drill bit through relatively large distances, up to six feet, by use of the drill bits known in the prior art. When drilling at a steep angle through a plurality of wall studs, for example, such a drill bit has a tendency to "walk", that is, trail off of the ideal path of travel, which would be a line extending axially forward from a longitudinal axis of the drill bit. This may be in part due to the asymmetric nature of the initial cutting edge of the prior art drill bits.
An elongated shank integrally connected to cutting head formed of three intersecting, equilateral triangles is seen in U.S. Pat. No. 3,121,351 to G. W. Mount. The three triangular planar end faces have a common intersecting point on the longitudinal axis of the shank. Three separate cutting edges, each formed by the line of intersection of two triangular surfaces, when cutting a wood surface, do not introduce any asymmetric forces into the drilling operation. However, this construction does not have the ability to traverse spaces between studs while maintaining the straight line axial movement desired. Furthermore, because the cutting head substantially fills the bore made by the drill, this construction results in decreased drilling efficiencies due to an inability to move wood shavings out of the way of the rotating cutting head.
A relatively flat cutting head assists in keeping wood shavings from interfering with the drilling operation, while a drill tip ending in a point allows a user of a drill bit to stick the drill bit into a piece of wood and self-start a hole. Both of these features are seen in U.S. Pat. No. 2,794,468 to Huxtable and U.S. Pat. No. 2,782,824 to Robinson, which show the use of a flat triangular point as a hole starter. Neither of these patents suggest the benefits of using a flat cutting tool with a triangular point in boring relatively long distances. The configurations of the drill bits shown in these patents induce a laterally extending cutting edge which makes at least a ninety degree angle with the longitudinal axis of the drill bit. Using the drill bit structure of either patent to cut through a remotely placed wall stud would result in asymmetric forces being applied to the rotating drill bit and would result in "walking" of the drill bit.